longest unique subsequence

private static int longestUniqueSubstring(String s){
        Map<Character, Integer> visitedCharsAndTheirIndices = new HashMap<>();
        int maxLen = 0;
        int currLen = 0;


        for(int i=1; i<s.length(); i++){
            char currElem = s.charAt(i);
            if(!visitedCharsAndTheirIndices.containsKey(currElem) || visitedCharsAndTheirIndices.get(currElem) < i - currLen){
                currLen++;
            } else{
                maxLen = currLen > maxLen ? currLen : maxLen;
                currLen = i - visitedCharsAndTheirIndices.get(currElem);
            }

            visitedCharsAndTheirIndices.put(currElem, i);

        }

        maxLen = currLen > maxLen ? currLen : maxLen;
        return maxLen;
    }